### 返回值:Array<Element(s)>:nth-child
### 概述
匹配其父元素下的第N个子或奇偶元素
':eq(index)' 只匹配一个元素，而这个将为每一个父元素匹配子元素。:nth-child从1开始的，而:eq()是从0算起的！可以使用:<br>nth-child(even)<br>:nth-child(odd)<br>:nth-child(3n)<br>:nth-child(2)<br>:nth-child(3n+1)<br>:nth-child(3n+2)
### 参数
#### **index**Number*V1.1.4*
要匹配元素的序号，从1开始
### 示例
#### 描述:
在每个 ul 查找第 2 个li
##### HTML 代码:
~~~
<ul>
<li>John</li>
<li>Karl</li>
<li>Brandon</li>
</ul>
<ul>
<li>Glen</li>
<li>Tane</li>
<li>Ralph</li>
</ul>
~~~
##### jQuery 代码:
~~~
$("ul li:nth-child(2)")
~~~
##### 结果:
~~~
[ <li>Karl</li>, <li>Tane</li> ]
~~~
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